Avalanche Forecast
Issued: Mar 28th, 2015 11:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Wind Slabs.
NWAC,
Northwest Avalanche Center
A mix of winter and spring avalanche conditions is likely above treeline east of the crest on Sunday.
Summary
Detailed Forecast
Southwest flow on the west side of an upper ridge will continue to carry frontal moisture mainly to BC through Sunday. Expect some occasional light showers in the Olympics and northwest Cascades with fairer conditions east of the crest and further south with moderate temperatures.
It is spring and despite the moderate temperatures the sun will have more effect on the snow pack. The main avalanche problem should be loose wet avalanches. Watch for possible wet surface snow deeper than a few inches, increasing snow balling or natural loose wet avalanches. While this problem should be mainly on solar slopes watch for it on all steep slopes. But this problem will be less extensive east of the crest where there has been less recent snowfall and rain.
Wind slab may linger on lee slopes mainly above tree line. Watch for possible firmer previously wind transported snow mainly on north to east aspects.
Cornices won't be listed as an avalanche problem. But avoid slopes below cornices and ridges or summits where cornices may be hard to see.
Less recent snow and ample terrain anchors will limit the avalanche danger below treeline. Many areas at the lowest elevations do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The 1-2 feet of snow that fell in mid-march east of the crest, mainly in the northeast Cascades, has settled or melted and likely been absorbed into the upper snowpack.
The DOT crew working at Washington Pass on Monday and Tuesday reports mostly stable overall snow conditions with 4-6 inches of recent snow above the pass and about 2 inches at pass level. One natural loose dry avalanche was seen at about 6500 feet on Silver Star Peak on Tuesday.
A warm front caused only light amounts of rain and snow Wednesday to Thursday morning with gradual warming along the east slopes. NWAC Observer Tom Curtis was on Nason Ridge on Thursday and reported small to medium rollerballs and evidence of recent small to large loose wet avalanches.
Sunshine and very warm temperatures Thursday and Friday caused more consolidation.
Snowdepths vary greatly across the east slopes with a regionally healthy snowpack in the northeast Cascades to bare solar slopes and lower elevation slopes in the central and southeast Cascades.
Problems
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Wind Slabs
Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 29th, 2015 11:00AM
